(1) Field of the Invention
This invention concerns a method and apparatus for sequentially nitrifying ammonia in landfill leachate ex situ and then returning the nitrified landfill leachate to the landfill for denitrification.
(2) Description of the Art
Landfill bioreactors as they are currently known and used are devices and constructions that enhance the aerobic and/or anaerobic degradation (fermentation) of municipal solid wastes. Currently available landfill bioreactors are flawed in that no attempt is made to control the cycling of inorganic forms of nitrogen present in the landfill waste material and present in the landfill leachate. As a result, the landfill leachate ammonia concentration increases over time creating leachate disposal problems and also aerobic and anaerobic microorganism poisoning where the ammonia containing leachate is recycled to promote landfill bioremediation.
Only a rare few landfills use denitrification processes to remove ammonia from landfill leachate. These facilities generally use sequential batch nitrification and denitrification reactors.
Generally, ammonia accumulation in landfill leachate has been ignored in the design of bioreactors. Thus, current landfill bioreactor design overlooks nitrogen cycle management. As a result, landfill bioreactors are prone to becoming unstable and uncontrollable due to ammonia accumulation in the wastewater. Therefore, landfill bioreactor designs that successfully manage the nitrogen cycle are needed.
It is an object of this invention to provide methods and apparatuses for managing the nitrogen cycle in a landfill bioreactor and, in particular, in managing landfill leachate ammonia.
It is another object of this invention to provide methods and apparatuses for controlling leachate ammonia in a manner that does not require ex-situ leachate disposal.
It is yet another object of this invention to provide methods and apparatuses for controlling the nitrogen cycle of a landfill bioreactor that promotes landfill bioremediation.
It is a further object of this invention to provide a method and apparatus for controlling the nitrogen cycle of a landfill bioreactor that minimizes the risk of landfill fires.
In one embodiment, this invention is a method for reducing the ammonia level of landfill leachate. The method begins by withdrawing ammonia containing leachate from a landfill. The ammonia containing leachate is directed into an attached growth nitrification unit. The ammonia containing leachate remains in the attached growth nitrification unit for a period of time sufficient to nitrify at least 50% of the ammonia in the leachate to form a nitrified aqueous product including nitrite and nitrate. Finally, the nitrified aqueous product is returned to the landfill or to another landfill where it is denitrified in situ.